When you compose a message, you should sign it. If it is business related, you may want to add additional contact information as well.
For example, your signature could read:
John Smith
Vice President of Engineering
Widgets Division
Acme Corporation, Inc.
303-555-1212 x111
john.smith@example.com
When you create your signature, you can enable to include your signature to all your messages automatically.
If you create a signature, but do not always want to use it, leave Add signature to all outgoing messages unchecked. When you compose a message, an Add Signature button appears in the toolbar. Clicking that button adds the signature you created to your message.
Open Options and select the Mail Identities tab.
Select the mail identity that you want and click the Signature tab, if you want your signature automatically applied to your message, check Add signature to all outgoing messages.
In the text box, type the signature information exactly as you want it to appear in your messages.
Specify the placement of the signature in your email message. Select Above included messages to add your signature at the end of the your composed, replied to, or forwarded text. Select Below included messages to add the signature at the end of the message.
Click Save.
The signature feature is available immediately. If you enabled to add your signature automatically, when you open a new compose window, your signature is added to the body of the message.